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Computational characterization of non-common iron III binding sites Agudelo, WA;Vazquez, DS;González Flecha FL;Santos, J; and González Lebrero, MC Department of Biological Chemistry and Institute of Biochemistry and Biophysics (IQUIFIB), School of Pharmacy and Biochemistry, University of Buenos Aires, Argentina. The motif (E/D)(E/D)xx(E/D)(E/D) is involved in iron exchange in the CyaY protein family and it is present in other metal ion binding proteins. Based on the C-terminal α-helix of E. colithioredoxin a model peptide containing the motif was synthesized and studied. This peptide shows iron III binding and induction of α-helical structure*. However the microscopic details of the motif-ion interactions are unknown. In this work the system was addressed by computational simulation techniques.The main goal was the characterizationof possible structures of metal peptide complex. Toobtain suitable peptide-ion structures, geometrical search was performed by genetic algorithm andthe most promising candidates were filtered by geometric criteria.Afterward, selected complexes were submitted to molecular dynamics simulations and the binding free energieswere computed by thermodynamic Integration and compared with experimental results from isothermaltitration calorimetry*.In addition, the protonation state of each residue of the motif was explored in the absence of the metal ion to evaluate a possible effect of clustering negatively charged residues on individual pKa values. * See submitted poster: ?Grafting a functional iron-binding motif onto a thioredoxin scaffold?. Acknowledgements: ANPCyT, UBACyT and CONICET for their support. References 1- Andreini C, Bertini I, Cavallaro G. et al. J. Mol. Biol. 2009. Vol. 388. pg356. 2- Seebeck B, Reulecke I, Kämper A. et al. Proteins. 2008. Vol 71, pg1237.

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